The present invention relates generally to the simultaneous interpretation and display of both a digital data stream and its underlying analog transmission signal. Such a simultaneous interpretation allows for the analyzing of any particular portion of the digital data, such as an error, and the underlying analog signal giving rise to the particular data, or error.
Data communications is the transmission of messages from one electronic device to other electronic devices. These messages are transmitted through a communications channel. A physical wire, optical cable, radio or other appropriate transmission medium may be used to implement the communications channel. A stream of individual data bits represents each message, thus comprising a digital data message. A communications protocol is an agreed-upon convention that defines the order and meaning of bits in a serial digital data stream. It may also specify a procedure for exchanging messages. A protocol will define how many data bits compose a message unit, the framing and formatting bits, error detection/correction bits, and any other information needed to transmit the message from the source to its destination, and to allow confirmation that the proper message was received on the receiving end.
When designing and building devices that communicate with each other to transmit messages therebetween, the builders must be aware that problems can occur during the transmission of the data, a device may incorrectly interpret a message, or a device may improperly respond to a received message. Tools are presently available for an individual to look at either the physical layer (comprising the actual received analog data signal) or the protocol layer (comprising the decoded digital data) separately. Protocol analyzers, for example, capture, decode, interpret, and react to the contents of data packets as they transit a network's media. They are typically concerned with layers 2 (Data Link) through 5 (Session) of the industry standard ISO/OSI Reference Model. However, they are blind to the shape and timing of the signals or Layer 1 (hardware, connections, etc). On the other hand, oscilloscopes and serial data analyzers allow the operator to accurately capture the data bits and view their shape as well as measure eye patterns, jitter, bit errors and other signal parameters such as rise time and overshoot for a wide variety of serial data standards which allow the operator to analyze the Layer 1, but do nothing for higher levels of the protocol stack. While some oscilloscopes now allow for a user to trigger on a specific serial analog data pattern so that a user can detect a predefined sequence of information, there has traditionally been no information provided above this physical layer as to the information content of the serial digital data stream represented by the captured analog waveform.
Attempts at providing correlated analog and digital data have been less than satisfactory. In one approach a serial data signal is displayed, and a cursor may define a portion of the serial data signal to be decoded to digital data in accordance with a predefined protocol. While this allows for the viewing of serial and same correlated digital data, this system has significant drawbacks. For example, the inventors of the present invention have determined that because there is no provision for triggering on a misinterpreted waveform, for example, it is not possible to monitor the digital data for an error in accordance with the defined protocol, and then view the portion of the analog signal corresponding to the digital error.